Change test/CodeGenCXX/debug-info-method.cpp an IR (rather than asm) test.

Referring back to the original commit (r115090) which was a frontend only test
I adjusted this test to verify the frontend change that was made, to emit the
protected access value in the flags metadata field.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171604 91177308-0d34-0410-b5e6-96231b3b80d8